|
Introduction
 
  • Classification
    • bacteria
      • gram-negative bacilli
        • the enterics
          • facultative anaerobes
            • lactose fermenting
              • Escherichia
                • E. coli
Pathogenesis
  • Transmission
    • endogenous
    • fecal-oral
    • contaminated food
      • undercooked meat
  • Reservoir
    • normal colonic flora
    • cow feces
  • Molecular biology
    • normal flora acquires virulence factors
      • pili 
        • P-fimbrae virulence factor is most important for colonization of urinary tract
      • exotoxin
        • LT
        • ST
        • shiga-like
      • endotoxin
        • lipid A part of LPS
      • K capsule  
        • K-1 capsular antigen allows meningeal infection
      • iron-binding siderophore
    • molecular mechanism of virulence depends on strain (see below)
Laboratory
  • Oxidase negative
  • Most E. coli ferment sorbitol
    • except EHEC which usually does not
  • Distinguish pathogenic strains via
    • immunoassay
    • serotyping
    • DNA probes
    • PCR
Clinical Conditions
  • Diarrhea
    • severity of diarrhea depends on strain ("PITcH")
    • virulence factors are shared between VibrioE. coli, and Shigella
      • EPEC ("pediatric")
        • second most common cause of diarrhea in infants
        • adherence to M cells prevents absorption
          • no toxin produced
        • developing countries
      • EIEC ("inflammatory")
        • bacteria invade epithelial cells
          • invasion and toxin act synergistically
        • virulence factor is shared by Shigella
        • blood and WBC in stool
          • like Shigellosis
      • ETEC ("traveler") 
        • LT (heat labile) toxin
          • similar to cholera toxin
          • ↑ cAMP
        • ST (heat stable) toxin
        • secretion of Cl- and HCO3- into intestinal lumen results in rice-water stools resembling those seen in cholera
      • EHEC ("hamburger")
        • Shiga-like toxin (verotoxin)
          • inhibits protein synthesis by inhibiting 60S ribosome 
        • no invasion of epithelium
          • virulence is only toxin-mediated
        • blood in stool
          • but no WBCs because no invasion
        • hemolytic uremic syndrome (HUS)
          • O157:H7 strain associated
          • classic triad
            • anemia
            • thrombocytopenia
            • acute renal failure
          • swelling of endothelium narrows lumen leading to
            • hemolysis
            • ↓ renal blood flow
            • ↓ platelets as damage is repaired
          • O157:H7 strain does not ferment sorbitol nor does it produce glucuronidase (vs. most other E. coli strains)
      • EAEC 
        • enteroaggregative E. coli
        • has the ability to adhere to intestinal cells
        • cause of traveler's diarrhea to less-developed countries
  • UTI
    • most common cause of UTI
    • acquisition of pili allows motility up the GU tract
    • ascending infection can cause pyelonephritis
  • Neonatal meningitis
    • second most common cause (vs. group B strep)
    • acquisition of K capsule inhibits phagocytosis to allow spread to meninges 
  • Sepsis
    • most common cause of Gram-negative sepsis
    • hospitalized patients
  • Pneumonia
    • hospital acquired
    • in neonates
  • Cystitis
  • Pyelonephritis
Treatment for Common Clinical Conditions Caused by E.Coli
EPEC diarrhea Supportive
EIEC diarrhea -----
ETEC diarrhea Rehydration with TMP/SMX
EHEC diarrhea Supportive (do not use antibiotics - they may cause HUS)
UTI Fluoroquinolones or sulfonamides
Neonatal meningitis Ceftriaxone
Sepsis Fluoroquinolones or 3rd generation cephalosporins

 

Please rate topic.

Average 5.0 of 6 Ratings

Questions (5)
EVIDENCE & REFERENCES (5)
Topic COMMENTS (13)
Private Note